1. Field of the Invention
The present invention relates a touch screen, a touch panel, and a display device including them.
2. Description of the Background Art
Conventionally, a touch panel that detects a touch made with an indicator such as a finger and identifies the position coordinates of the touch is attracting attention as one of excellent interface means. For this touch panel, various types including resistive types and capacitive types have been proposed and put into practice as commercial products.
As one kind of such capacitive type touch panels, a projected capacitive type touch panel is known, as disclosed in National Publication of Translation No. 9-511086 (1997). In this projected capacitive type touch panel, even when a front surface side of a touch screen having a touch sensor built therein is covered with a protection plate such as a glass plate having a thickness of about several mm, a touch to the protection plate with a finger, or the like, can be detected. This touch screen is advantageous in that it has excellent robustness, in that a touch can be detected even when a user wears gloves, in that no movable part is provided and therefore a long life is ensured, and so on. Therefore, various techniques therefor are proposed.
For example, a touch screen provided in a touch panel disclosed in National Publication of Translation No. 9-511086 (1997) includes, as a detection wire (detection electrode) for detecting an electrostatic capacitance, a first series conductive element and a second series conductive element. The first series conductive element is formed as a thin conductive film. The second series conductive element is formed on the first series conductive element with interposition of an insulating film therebetween. No electrical contact is made between the conductive elements, but a plurality of crossing points are formed therebetween. In this technique disclosed in National Publication of Translation No. 9-511086 (1997), an electrostatic capacitance formed between an indicator such as a finger and the conductive elements serving as the detection wire is detected by a detection circuit, and thereby position coordinates of a position touched with the indicator is identified. Furthermore, by using relative values of detected capacitances among one or more conductive elements, a touch position can be interpolated among the conductive elements.
A touch screen provided in a touch panel disclosed in Japanese Patent Application Laid-Open No. 2010-61502 includes a detection column wire and a detection row wire. Each of the wires is formed as a metal wire in a zigzag pattern such that the metal wire is repeatedly staggered with an inclined portion that is inclined at 45° in each of column and row directions. In this technique disclosed in Japanese Patent Application Laid-Open No. 2010-61502, the density of wires can be increased and thereby the sensitivity of touch detection can be improved, without increasing a parasitic capacitance between the detection wires.
A touch screen provided in a touch panel disclosed in Japanese Patent Application Laid-Open No. 2010-97536 includes a detection column wire and a detection row wire that are formed in a zigzag pattern, similarly to the touch screen disclosed in Japanese Patent Application Laid-Open No. 2010-61502. Additionally, the touch screen provided in the touch panel disclosed in Japanese Patent Application Laid-Open No. 2010-97536 further includes a wire between the detection column wire and the detection row wire.
National Publication of Translation No. 2003-526831 discloses a detection type generally called a mutual capacitance detection type. More specifically, a key matrix disclosed in National Publication of Translation No. 2003-526831 is composed of an array of a plurality of pairs of driving/receiving electrodes. A change in a coupling capacitance (capacitance between electrodes) involved in a change in an electric field between electrodes, which occurs in accordance with a contact to a substrate with an indicator such as a finger, is detected as the amount of charge.
A capacitance-based touch detection device disclosed in National Publication of Translation No. 11-505641 (1999) is provided with an electrode array including an X electrode and a Y electrode. A mutual capacitance between the X electrode and the Y electrode is detected by a capacitance measurement circuit. Then, a change in an output voltage indicating the measured capacitance is determined in accordance with a mutual capacitance, a known reference capacitance, a known change in a driving voltage.
The techniques disclosed in Japanese Patent Application Laid-Open No. 2010-61502 and Japanese Patent Application Laid-Open No. 2010-97536 mentioned above can increase the density of wires without increasing an inter-wire capacitance (hereinafter, “capacitance between row and column wires”) formed between the detection column wire and the detection row wire. The detection wire arranged in a rectangular shape is advantageous in that a coordinates interpolation process based on a result of detection is more readily performed than a detection wire arranged in the shape of linked diamonds, or in that the linearity of coordinates obtained as a result of an interpolation process is high (particularly in an oblique direction).
In some detection methods, the capacitance between row and column wires, which changes in accordance with the presence or absence of a touch to a touch screen with an indicator such as a finger, is intimately associated the sensitivity of detection. For example, in the mutual capacitance detection type disclosed in National Publication of Translation No. 2003-526831, as a change in a capacitance between row and column wires (a change in the electric field between the electrodes) which occurs in accordance with a touch with an indicator such as a finger is higher, a higher sensitivity of detection is obtained.
However, in a case where a capacitance (electric field coupling) between the column direction wire bunch and the row direction wire bunch is high, for example, in a case where the detection method disclosed in Japanese Patent Application Laid-Open No. 2010-97536 is applied to the touch screen disclosed in Japanese Patent Application Laid-Open No. 2010-61502, it is not likely to cause a change in the electric field between the detection column wire and the detection row wire, that is, a change in the capacitance between row and column wires, which otherwise occurs in accordance with a touch with an indicator such as a finger. Accordingly, application of the mutual capacitance detection type to such a configuration causes a problem that the sensitivity of detection of a touch is low.